Heating device

ABSTRACT

A heating device incorporated in an article of clothing or a shoe, notably a ski boot, comprising a sealed enclosure (2) in contact with the area of the body to be heated, this enclosure containing a salt (5) which changes phase between solid and liquid and has a latent fusion heat close to the normal temperature of the area of the body, from 30° to 40° C., and in which the heating resistance (6) is in a heat exchange with the salt contained in the sealed enclosure (2) such that after heating of the salt, as it returns to its solid state, it progressively gives off heat for a long period of time, while maintaining a substantially constant comfortable temperature.

This application is a continuation of application Ser. No. 086,986,filed 08/19/87 now abandoned.

FIELD OF THE INVENTION

The present invention is a heating device incorporated in an article ofclothing or a shoe, notably a ski boot.

BACKGROUND OF THE INVENTION

We already know of heating devices incorporated in articles of clothingsuch as gloves or in other clothing or in shoes, notably ski boots.These devices generally comprise an electrical heating resistanceconnected to a battery or a cell through a switch which can be shut offmanually or automatically under the control of a system of temperatureregulation including a temperature sensor. Such an electrical resistanceheating device has the drawback that the cells used to supply theelectricity for the heating resistance are used up very quickly, sincethe resistance must be used frequently in order to to maintain a desiredcomfortable temperatures.

SUMMARY OF THE INVENTION

The present invention aims to overcome the drawback by using a heatingdevice of particularly simple conception, and by ensuring themaintenance of a comfortable temperature for a long period of time atthe cost of a low consumption of electrical energy.

To this end, this heating device, incorporated in an article of clothingor a shoe, notably a ski boot, including an electrical heatingresistance connected, through a switch, to a source of electricalcurrent, this heating resistance being placed near a section of the bodyto be heated, has a sealed enclosure in contact with the section of thebody to be heated, this enclosure containing a salt which changesbetween liquid and solid phase and has a latent fusion heat of atemperature close to the normal temperature of the section of the body,from 30 to 40° C., and in which the heating resistance is in a relationof heat exchange with the salt contained in the sealed enclosure suchthat the electrical current of the heating resistance, in a short periodof time, causes the salt contained in the sealed enclosure to enter aliquid state, after which this salt, in returning to the solid state,progressively gives off heat over a long period of time, therebymaintaining a substantially constant comfortable temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be more clearly understood, referencewill now be made to the attached drawings in which several embodimentsof the invention are shown for purposes of illustration, and in which:

FIG. 1 is a vertical and longitudinal schematic section of a ski bootequipped with a heating device according to the invention.

FIG. 2 is a diagram which illustrates the operation of the heatingdevice according to the invention.

FIG. 3 is a vertical and cross-wise sectional view of a secondembodiment of the heating device according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 represents a ski boot 1 in the interior of which incorporates aheating device according to the invention. This heating device includesa sealed enclosure 2 which is placed on the insole of the shoe, insidethe normally used inner casing. This sealed enclosure 2 can beconstituted by two elements, namely a plate with a rigid base 3, and awall 4 of flexible material applied against the area to be heated andhaving good heat conductivity. The sealed enclosure 2 contains a certainquantity of salt 5 which changes between liquid and solid phase and hasa latent fusion heat and this salt is chosen so that this change ofphase takes place at a temperature near the normal temperature of thearea to be heated, i.e., from 30 to 40° C.

Additionally, the sealed enclosure 2 contains an electrical heatingresistance 6 which is connected, by electrical conductors, to a currentsource 7, such as a cell or a battery, through a switch 8.

By way of example, the heating device according to the invention coulduse, as a phase-changing salt with latent fusion heat, disodium hydrogenphosphate (Na₂ HPO₄. 12H₂ O), which has a fusion temperature of 33.5° C.The sealed enclosure 2 could contain for example 25 grams of this salt.The resistance 6 could have a value of 2.6 ohms, the heated surface areabeing 3000 mm², while the heating surface of the electrical conductor is1100 mm². The supply of electrical current can come from twoaccumulators of the Ni-Cd type with an electrical potential of 2.4 V anda capacity of 1.2 AH. The base plate 3 of the sealed enclosure 2 is madeof a sheet of polyvinyl-polyethylene chloride with a thickness of 500micrometers having average heat conductivity and good mechanicalresistance. The upper wall 4 is made of a film of polyamide-polyethylenewith a thickness of 50 micrometers having a very good heat conductivity.

To use the heating device when the need arises, the skier closes theswitch 8 which has the effect of triggering the supply of electricalcurrent of the heating resistance 6 incorporated inside the sealedenclosure 2. The heat given off by the resistance 6 causes a progressiverise in the temperature in the interior of the sealed enclosure 2, atemperature whose variation is indicated by the full-line curve, asshown in FIG. 2, starting from the ambiant temperature which is presumedto be 20° C. The electrical resistance 6 furnishes by Joule's Effect theamount of heat necessary to cause the salt 5 to pass from solid phase toliquid phase. In the particular case considered by way of example, inwhich the sealed enclosure contains 25 grams of disodium hydrogenphosphate, it is determined that at the end of 30 minutes the salt haspassed entirely into the liquid phase, and at this moment, the heatingis turned off by opening the switch 8. The heating period, i.e., theperiod during which electricity flows through the electrical resistance6, is indicated by Zone A in FIG. 2. At the end of this period, thetemperature attained equals about 40° C. After the heating is cut off,the salt 5 returns progressively to the solid state, releasing its heatfor about one hour. As seen in FIG. 2, the temperature falls very slowlythroughout this one-hour period, remaining close to the comforttemperature of 35°.

By way of comparison, the temperature variation curve has been shown asa function of time when only the resistance heat (direct heating) isused (broken lines on FIG. 2). After 30 minutes of heating, thetemperature attained is 80°, the inertia of the resistance providesabout another 20 minutes of heat and the temperature falls back to 30°at the end of this period. The effect of the heating is thus shorter andmore violent than in the case when one uses the salt 5 with latentfusion heat.

Another advantage obtained by means of the heating device according tothe invention is that, if the temperature at which the phase changeoccurs is exactly the same as the normal temperature of the foot, anadjustment of the latter temperature is produced automatically. Ineffect, if the foot is too hot, the salt absorbs the excess calories bypassing to the liquid state while on the other hand if the foot becomestoo cold, the salt returns to the solid state by releasing calories.

To avoid the salt 5 in liquid phase spilling under the toes, itsdisplacement can be limited by incorporating it in a gel incorporated inthe interior of the sealed pouch 2 to act as a sponge.

While the preceding indicated that the heating device 2,6 is placedunder the toes of the foot, it is evident that it could be placedanywhere in the shoe and that it could in particular be formed as acomplete insole placed in an inner shell which will assure that theimpression of the plantar support of the skier will be made during thesolidification of the mixture in the enclosure 2.

In the embodiment shown in FIG. 3 the sealed enclosure 2 is the upperpart 9 of the insole 10 which contacts the foot, while the lower part 11of this insole, to which the upper sealed enclosure 5 is attached, ismade of a heat insulating material.

The heating device according to the invention can be incorporated in anyarticle of clothing, notably in a glove, a helmet and any otherwearables.

It is possible to include a temperature display and a temperature gaugewhich would permit the automatic triggering of the electrical heatingresistance when the temperature of the body area to be heated fallsbelow a predetermined level.

What is claimed is:
 1. A heating device incorporated in an article ofwear, notably a ski boot, comprising an electrical heating resistanceconnected, by a switch, to a current source, said heating resistancebeing located adjacent a foot to be heated, said device comprising asealed enclosure (2) in contact with said foot, containing a salt (5)which changes phase between liquid and solid and has a latent fusionheat of a temperature close to the normal temperature of said foot inthe range of 30° to 40° C., said heating resistance (6) being in a heatexchange relation with said salt and constituting means for liquefyingsaid salt by heat exchange for a short period of time, termination ofsaid heat exchange causing said salt to return to a solid state,releasing heat progressively over a prolonged period of time, whilemaintaining a substantially constant comfortable temperature.
 2. Adevice according to claim 1, wherein said sealed enclosure (2) comprisesa rigid base plate (3) and a wall (4) of flexible material appliedagainst said foot and having good heat conductivity.
 3. A deviceaccording to claim 1, wherein said salt is constituted by disodiumhydrogen phosphate (Na₂ HPO₄. 12 H₂ O), which has a fusion temperatureof 35.5° C.
 4. A device according to claim 1, wherein said salt (5) isincorporated in a gel placed inside said sealed enclosure (2) and actsas a sponge.
 5. A device according to claim 1, wherein said sealedenclosure (2) constitutes an upper part (9) of an insole (10) contactingsaid foot, a lower constitutive part (11) of said insole, to which saidsealed enclosure (5) being attached, is made of heat insulatingmaterial.
 6. Process for heating a foot housed in footwear, comprisingthe steps of(a) providing a heating resistance in said footwear adjacentsaid foot; (b) providing a sealed enclosure in contact with said foot,said enclosure containing a salt which changes phase between liquid andsolid and has a latent fusion heat of a temperature close to the normaltemperature of said foot, in the range of 30° to 40° C., said heatingresistance being in heat exchange relation to said salt; (c) passing anelectrical current through said heating resistance for a first period oftime sufficient to cause said salt to pass from solid phase to liquidphase; (d) terminating passage of said electrical current when said salthas passed entirely into liquid phase, whereby said salt returnsprogressively to solid state over a second period of time of greaterduration than said first period of time, releasing stored up heat so asto cause heating of said foot.